LONDON - The proportion of women with early-stage breast cancer receiving incorrect treatment in the United States has nearly doubled in the 1990s, increasing from 12 percent in 1989 to 22 percent by 1995, a new study says. The reason is the growing popularity of lumpectomy, where doctors cut out only the cancerous part of the breast instead of removing the whole breast, and the failure of some doctors to carry out important follow-up treatments, said the study, published this week in The Lancet medical journal.

It estimated that about 22,000 American women each year may be receiving substandard care.

Two treatment options are considered appropriate when breast cancer has not spread to other areas. The first is a mastectomy the removal of the breast together with a dissection of the lymph nodes in the armpit to ensure they are cancer free.

The second is a lumpectomy, along with the lymph node check and radiation treatment of the area. Although it allows women to keep their breasts and can be as effective at eliminating cancer if done right, lumpectomy is a more complicated treatment than mastectomy.

The problem noted by researchers from the Medical College of Wisconsin in Milwaukee was that some doctors skipped the radiation or lymph node inspection, or both, when they performed lumpectomies.

Dr. Ian Fentiman, a professor of oncology at Guy's Hospital in London, said a similar trend of substandard lumpectomies was seen in Britain.

"The mortality rate from breast cancer is falling as a result of earlier diagnosis and better treatment and it is very important that this success is now not compromised by inadequate treatment," said Fentiman, who was not connected with the research.

In the study, the scientists examined the medical records of 144,759 women aged 30 and older who had surgery in the United States for early-stage breast cancer between 1983 and 1995.

In 1990, experts agreed at a National Institutes of Health consensus conference that lumpectomy is the preferable approach and set out the recommended procedures for both options. Since then, lumpectomy has been on the rise.

The researchers found that the proportion of women getting substandard lumpectomy treatment increased from 10 percent in 1989 to 19 percent at the end of 1995.

Meanwhile, the proportion of women whose mastectomy treatment was performed incorrectly remained steady at 2.7 percent during the time of the study, which means the decline was connected to lumpectomies.

Overall, the proportion of women getting the correct treatment declined from 88 percent in 1989 to 78 percent in 1995.

The study concluded that the problem is not that doctors are getting more lax when performing lumpectomies, but that more women overall were getting lumpectomies instead of mastectomies.

While about 15 percent of women got lumpectomies in 1983, about half were getting that treatment by 1995.

Some doctors or patients might disagree with the recommended methods, so it is not surprising that some women are not getting the standard treatment, the study said.

"What is surprising, however, is that the proportion of the population meeting the standard declined in the years immediately after" the 1990 NIH recommendations on standards for treatment, the study said.